The combination, aspirin-salicylic acid-salicyluric acid, was tested in rabbits and rats as a possible precursor-drug-metabolite combination suitable for measuring functional hepatic flow. C14-aspirin and H3-salicylic acid were infused iv at a constant rate. This precursor-drug-metabolite combination was unsatisfactory for measuring hepatic blood flow, because the renal clearance of salicyclic acid was low (less than 3 ml/min/kg).